Pres09 - Electrical Hazards 3-02

Suggestion on How to Use • Industry Trainers are encouraged to use this material in their sessions • Download both the PowerPoint file (.ppt) and script file (.pdf) • Print the script file (.pdf) and read the script as you view the PowerPoint presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (if there is any) • Must have PowerPoint and Adobe Reader application software on your system.

Electrical Hazards

Safety BASICs

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Basic electrical theory I=V/Z •What happens with shock? •What happens when have fault? •What happens with larger transformers or low impedance transformers? •What is difference between short-circuit and arcing fault?

Safety BASICsTM Who’s Responsible for Safety? The “Employer” is responsible for OSHA requirements Electrical Safety Program Safety Policies and Procedures Safety Training The “Employee” is responsible for Implementing procedures The “Owner” is inherently responsible for Contractors on site

Safety BASICs

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What are the hazards as you approach electrical equipment to perform work?

Safety BASICs

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Are you thinking that the National Electrical Code and UL Standards are sufficient to protect a person working on or near “live” equipment?

Safety BASICs Product Standards NEMA Underwriters Lab. IEC (Electrotechnical committee)

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National Electrical Manufacturers Association

Example of UL 508 – Testing only w/ door closed

Safety BASICs

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Installation Standards National Electrical Code® National Electrical Safety Code® National Electrical Contractors Association IEC (International -60364)

National Electrical Code

1997 ANSI/NFPA 70

NFPA 70E • Requirements for safe work practices • Addresses hazards: – Shock – Arc Flash • Requirements for shock and arc flash boundaries • Requirements personal protective equipment

NFPA 70E: Safety in Workplace OSHA 1910.333 (a) (1) & NFPA 70E 2-1.1.1 Qualified electrical workers shall not be asked to work on equipment that is “hot” or “live” except for two demonstrable reasons :

or

1. Deenergizing introduces additional or increased hazards such as cutting ventilation to a hazardous location 2. Infeasible due to equipment design or operational limitations such as doing voltage testing for diagnostics

Safety BASICs

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Electrical Hazards • Shock • Arc-Flash – Heat – Fire • Arc-Blast – Pressure – Shrapnel – Sound

Example of an arcing fault

Safety-Related Work Practices 1910.333 Selection & use of work practices (a) General. Safety-related work practices shall be employed to prevent electric shock or other injuries resulting from either direct or indirect electrical contact, when work is performed near or on equipment or circuits which are or may be energized. The specific safety-related work practices shall be consistent with the nature and extent of the associated electrical hazards

Safety-Related Work Practices 1910.335 Safe guards for personnel protection (a) (2) (B) (ii) Protective shields, protective barriers, or insulating materials shall be used to protect each employee from shock, burns, or other electrically related injuries while that employee is working near exposed energized parts which might be accidentally contacted or where dangerous electric heating or arcing might occur.

Safety BASICs

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Shock Over 30,000 non-fatal electrical shock accidents occur each year Over 600 people die from electrocution each year Electrocution remains the fourth (4th) highest cause of industrial fatalities Most injuries and deaths could be avoided

Safety BASICs Shock (Resistance Table)

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Safety BASICs

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Shock

(A) Touch Potential

(B) Step Potential

(C and D) Touch / Step Potential

Current passing through the heart and lungs is the most serious

Safety BASICs

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Shock Human body resistance (hand to hand) across the body is about 1000Ω Ohms Law: I = V / R (Amps.) I = 480 volts / 1000 Ω = 0.48 amps (480 mA) The National Electrical Code® considers 5 mA to be the safe upper limit for children and adults.

Safety BASICs

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Shock Current, Not Voltage causes Electric Shock

mA

Affect on Person

0.5 - 3

- Tingling sensations

3 - 10

- Muscle contractions and pain

10 - 40

- “Let-go” threshold

30 - 75

- Respiratory paralysis

100 - 200

- Ventricular fibrillation

200 - 500

- Heart clamps tight

1500 +

- Tissue and Organs start to burn

Note: Reaction will vary with frequency and time of exposure

Safety BASICs

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Arc-Flash As much as 80% of all electrical injuries are burns resulting from an arc-flash and ignition of flammable clothing Arc temperature can reach 35,000°F - this is four times hotter than the surface of the sun Fatal burns can occur at distances over 10 ft. Over 2000 people are admitted into burn centers each year with severe electrical burns

Electrical Arc 35,000 °F

Molten Metal Pressure Waves Sound Waves

Copper Vapor: Solid to Vapor Expands by 67,000 times

Shrapnel Hot Air-Rapid Expansion Intense Light

Personnel Hazards Associated with Arc Flash Heat – Burns & Ignition of Materials Arc temperature of 35,000 ºF Molten metal, copper vapor, heated air Second Degree Burn Threshold : 80 ºC / 175 ºF (0.1 sec), 2nd degree burn Third Degree Burn Threshold: 96 ºC / 205 ºF (0.1 sec), 3rd degree burn Intense Light Damage eyes – cataracts

Personnel Hazards Associated with Arc Flash Pressures From Expansion of Metals & Air Eardrum Rupture Threshold 720 lbs/ft2 Lung Damage - Threshold 1728 - 2160 lbs/ft2 Shrapnel Flung Across Room or From Ladder/Bucket

IEEE/PCIC & NFPA 70E Arc Flash Hazard

IEEE/PCIC • Users • Consultants • Manufacturers • Medical Experts

Arc Flash Hazard • Following are some of the tests run by IEEE Ad Hoc Safety Committee • All of the devices used for this testing were applied according to their listed ratings

Setup Area For Tests #1 Through #4

Arc-Flash

Close-up of Test Area

Test No. 4

22.6 KA Symmetrical Available Fault Current @ 480V, 3 Phase

6 cycle STD Set @ 6 cycle opening

640A OCPD Non Current Limiting with Short Time Delay

Fault Initiated on Line Side of 30A Fuse 30A RK-1 Current Limiting Fuse Size 1 Starter

TEST 4

TEST 4

TEST 4

TEST 4

TEST 4

TEST 4

TEST 4

Results: Test No. 4

22.6 KA Symmetrical Available Fault Current @ 480V, 3 Phase

Opened in six cycles No Current Limitation

Fault Initiated on Line Side of 30A Fuse

640A OCPD Non Current Limiting with Short Time Delay

30A RK-1 Current Limiting Fuse Size 1 Starter

Results: Test No.4 Sound

141.5 db @ 2 ft.

P1

T2

>2160 lbs/sq.ft

> 225 C /437 F T3 50 C / 122 F

T1 > 225 C / 437 F

> Indicates Meter Pegged

Test No. 3

22.6 KA Symmetrical Available Fault Current @ 480V, 3 Phase

601A. Class L Current Limiting Fuse

Fault Initiated on Line Side of 30A Fuse

30A RK-1 Current Limiting Fuse

Size 1 Starter

TEST 3

TEST 3

TEST 3

TEST 3

Results: Test No. 3 Cleared in 1/4 Cycle Current-Limitation Reduced Energy

Fault Initiated on Line Side of 30A Fuse

22.6 KA Symmetrical Available Fault Current @ 480V, 3 Phase

601A. Class L Current Limiting Fuse

30A RK-1 Current Limiting Fuse

Size 1 Starter

Results: Test No.3 Sound

133 db @ 2 ft.

P1

T2 62 C / 143.6 F

504 lbs/sq.ft.

T3 (No Change From Ambient)

T1 > 175 C/ 347 F

> Indicates Meter Pegged

Test No. 1

22.6 KA Symmetrical Available Fault Current @ 480V, 3 Phase

601A. Class L Current Limiting Fuse

30A RK-1 Current Limiting Fuse

Fault Initiated on Load Side of 30A Fuse

Size 1 Starter

X

TEST 1

TEST 1 Close-up

TEST 1 Close-up

TEST 1 Close-up

TEST 1 Close-up

TEST 1 Close-up

22.6 KA Symmetrical Available Fault Current @ 480V, 3 Phase

Results: Test No. 1

Class L Fuse Did Not Open, System was Selectively Coordinated

30 A RK-1 Fuse Cleared Fault in Less Than 1/4 Cycle

601A. Class L Current Limiting Fuse

30A RK-1 Current Limiting Fuse Size 1 Starter

Fault Initiated on Load Side of 30A Fuse

Results: Test No.1 Sound (No Change From Ambient)

T2 (No Change From Ambient)

T3 (No Change From Ambient)

P1 (No Change From Ambient)

T1 (No Change From Ambient)

Safety BASICs

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Current-Limitation - Arc-Energy Reduction Available Fault Current

Reduced Fault Current

Non-Current Limiting

Current Limiting

Consider that: • Magnetic Force -- varies with the square of the Peak Current • Thermal Energy -- varies with the square of the RMS Current

Safety BASICsTM Current-Limitation: Arc-Energy Reduction Test 4

Test 3

Non-Current Limiting

Reduced Fault Current via Current-Limitation

Test 1

Safety BASICs

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What are the hazards as you approach electrical equipment to perform work? • Shock • Arc Flash • Arc Blast

Safety Basics Video (VHS)